Design, Synthesis, and Pb 2+ ‐Selective Optical Sensing Properties of Novel π‐Conjugated Dibenzosuberenone–Dihydropyridazine Fluorophores

ABSTRACT Herein, five new π‐conjugated small organic molecules ( DD1‐DD5 ) were synthesized starting from dibenzosuberone ( 1 ), applying a modular approach based on Suzuki coupling and Diels–Alder/ retro ‐Diels–Alder (DA/ r DA) reactions. The key intermediate, dibromodibenzosuberenone 4 , was obtained in three steps, and its Suzuki couplings with aryl and heteroaryl boronic acids furnished compounds 10‐12 . A Sonogashira‐type modification of compound 4 enabled the preparation of the diacetylene derivative 14 , which, together with compounds 10‐12 , was reacted with tetrazines 20 and 22 via DA/ r DA reactions to afford the target cycloadducts DD1‐DD5 . All compounds were characterized by NMR, FT‐IR, and HRMS analyses. UV–vis and fluorescence studies demonstrated that all DD1‐DD5 derivatives exhibited pronounced selectivity and high sensitivity toward Pb 2+ ions, showing distinct absorbance changes, strong turn‐on emission, and >100 nm mega‐Stokes shifts. DD1 displayed the most significant Pb 2+ response, while electron‐withdrawing groups of DD4 (–NO 2 ) and DD5 (–CF 3 ) modulated their optical behavior. Additional but weaker selectivity toward Fe 3+ was observed for DD4 and DD5 . Job plot analysis indicated 1:1 binding for DD1‐DD2 and 2:1 Pb 2 + –ligand stoichiometry for DD3‐DD5 . 1 H NMR titrations supported Pb 2+ complexation and revealed multi‐dentate binding, particularly for DD3 . Overall, the DD scaffold provides a tunable platform for selective Pb 2+ sensing with complementary anion‐responsive behavior.